1. Field of the Invention
This invention relates to a method and circuit for quickly starting a negative switching voltage regulator to reach a certain level of negative voltage.
2. Background Information.
A typical negative switching voltage regulator is one which employs a switching voltage regulator chip, like chip TL497, which is manufactured by Texas Instruments, for example. The regulator chip is used in a circuit which has a output terminal from which the regulated negative voltage is obtained. The regulator chip includes a start terminal and an internal switching transistor which switches "on" and "off" to provide current to other elements included in the circuit. As soon as an energizing signal is placed on the start terminal, the switching transistor starts to switch on and off, and during this start-up time, the voltage on the output terminal of the circuit begins to increase in a negative direction.
One of the problems with a typical prior art negative switching voltage regulator of the type mentioned is that the negative output voltage typically can take up to 10 seconds to reach its predetermined level. If, for example, a liquid crystal display (LCD) is operated from the negative voltage, during the 10 seconds that the voltage is increasing to the predetermined level, the LCD and the terminal in which the LCD is located may be considered inoperative. In some situations, the negative voltage from the circuit may not reach the desired negative level at all.